The antenna connected to electronic components of wireless or contactless communication devices is tuned to a frequency compatible with contactless communication of information. Such a frequency may be, for example, a resonance frequency equal to a carrier frequency, e.g., 13.56 MHz, or a resonance frequency contained in a permissible range around the carrier frequency.
Such components are sometimes referred to as “contactless components” and may be, for example, near field communication (NFC) components, i.e., components compatible with NFC technology.
The NFC component may be, for example, an integrated circuit or chip, incorporating an NFC microcontroller.
The acronym NFC designates a high frequency, short distance wireless communication technology, which makes the exchange of data possible between two contactless devices over a short distance, e.g., 10 cm.
NFC technology is standardized in documents ISO/IEC 18 092, ISO/IEC 21 481 and NFC FORUM but incorporates a variety of pre-existing standards including Type A and Type B protocols of the standard ISO/IEC 14 443.
An NFC component may generally be used either in “reader” mode or in “card” mode for communicating with another contactless device, e.g., by using a contactless communication protocol such as the Type A protocol of the standard ISO/IEC 14 443.
In the “reader” mode, the NFC component acts as a reader with respect to the external contactless device which may then be a card or a label. In the reader mode, the NFC component may then read the contents of the external device and write information to the external device.
In the “card” mode, the NFC component then behaves as a transponder, e.g., a card or a label, and communicates with the external device which this time is a reader.
The transponder may be passive or active.
A passive transponder performs a load modulation of the magnetic field generated by the reader.
An active transponder uses an active load modulation (also known to the person skilled in the art under its acronym ALM) for transmitting information to the reader. The transponder also generates a magnetic field via its antenna which simulates the load modulation of the field of the reader performed by a passive transponder.
Active load modulation is advantageously used when the signal resulting from a passive load modulation is not strong enough to be detected by the reader. This is notably the case when the antenna of the transponder is small or located in an unfavorable environment.
An NFC component or chip may, for example, be incorporated in a mobile cellular phone, and the latter may then be used, in addition to its conventional telephone function, for exchanging information with the external contactless device.
Numerous applications are thus possible, such as crossing a toll barrier in transport (the mobile phone acts as a transport ticket) or payment applications (the mobile phone acts as a credit card).
Active transponders may be specific devices, e.g., contactless smart cards, integrated circuit (IC) cards, labels or badges, or contactless devices or components emulated in card mode, here again, for example, incorporated into host apparatuses such as, for example, mobile cellular phones or tablets.
Contactless components or chips, such as NFC components or chips, are generally connected to the antenna via an impedance matching circuit in order to optimize radio frequency communication. And, the elements used in this impedance matching circuit, e.g., coils and capacitors, are dimensioned so as to make a correct frequency tuning of the antenna possible, e.g., on a carrier frequency, (e.g., 13.56 MHz), and thus to ensure maximum performance.
Furthermore, a contactless component or chip generally includes a driving stage for driving the antenna, which is connected to the terminals of the antenna via the impedance matching circuit, making it possible for a current with the carrier frequency considered (e.g., 13.56 MHz) to be made to flow in the antenna so as to generate the electromagnetic field.
This driving stage generally includes a driving circuit (commonly designated by the person skilled in the art as a “driver”) which is preferably supplied with a voltage via a regulator with a low drop out voltage, which commonly designated by the person skilled in the art as a low drop out (LDO) voltage regulator.
For reasons of interoperability, contactless communication standards, e.g., the NFC FORUM standard, require that the transfer of power between a reader and a transponder falls within a certain power range.
When the power transmitted through the antenna of a reader or an active transponder exceeds this range, e.g., when the reader and the transponder are too close, a dynamic power control (DPC) is implemented to reduce this transmitted power.
This reduction in power may also be required by the transponder itself by sending a specific request to the reader, when the transponder supports this functionality which is provided for in the Dynamic Power Level Management (DPLM) amendment of the standard ISO/IEC 14 443.